More Information:

Multi-Step ApproachThe VIMS report calls for a flexible, "staircase" approach for adapting to coastal flooding. Here's an example of such an approach for an urban area.

Multi-Step ApproachThe VIMS report calls for a flexible, "staircase" approach for adapting to coastal flooding. Here's an example of such an approach for a rural area.

Flooding Depth SimulationAn example of a flooding-depth simulation map from the VIMS report. See report for higher resolution maps for this and other areas.
Image courtesy of CCRM.

Potential Flooding ZonesAn example of a map showing potential flooding zones under different scenarios of sea-level rise. See the VIMS report for higher resolution maps for this and other areas.
Image courtesy of CCRM.

Road FloodingFrequency of flooding of VDOT-maintained roads in Tidewater Virginia. See VIMS report for higher resolution map.
Image courtesy of CCRM/Data from VDOT.

VIMS calls for flexible, multi-step approach to deal with flood risk

Researchers present coastal flooding
report to General Assembly

Recurrent coastal flooding—think Isabel, Ernesto, Irene,
Sandy, the “Son of Ida,” and numerous other unnamed nor’easters—is a
significant and growing threat to the people and places of Tidewater Virginia.

The report makes clear that no single response will fully
address the complex web of social, legal, and environmental issues that
contribute to Tidewater’s vulnerability to coastal flooding. Instead, it calls for
a multi-step approach with enough flexibility to allow policymakers to adapt as
conditions change and knowledge grows. It also says the time for action is now.

The report—Recurrent
Flooding Study for Tidewater Virginia—is the result of a yearlong effort by
researchers in VIMS’ Center for Coastal Resources Management. The study was led
by Ms. Molly Mitchell and CCRM Director Carl Hershner, with input from an
advisory panel that included colleagues at VIMS, Old Dominion University, the W&M
Coastal Policy Clinic, the Hampton Roads Planning District Commission, the
Accomack-Northampton Planning District Commission, Wetlands Watch, relevant
state agencies, as well as cities and counties throughout eastern Virginia.

The study’s authors collected data and analyses from agencies
at the local, state, and federal levels, as well as from non-governmental
organizations and regional authorities such as the Chesapeake Bay Program. They
also reviewed a comprehensive list of strategies used in other vulnerable areas
around the U.S. and world, including New Orleans, the Netherlands, the United
Kingdom, Japan, and other smaller Pacific islands.

Findings and Recommendations

“Recurrent flooding is already a significant issue in Virginia’s
coastal zone, and is predicted to become even worse over reasonable planning
horizons,” says Mitchell. “Our review of strategies already being used in other
vulnerable areas suggests that the Commonwealth can mount an effective response to its increasing flood risk, but that
we must start now, as it will take 20 to 30 years to effectively plan and
implement many of the adaptive measures.”

Hershner says the optimal strategy will be “to develop flexible
plans that match adaptation options to the unique circumstances of each coastal
locality, and that link the implementation of those options to the changing
risks.”

Adaptation Options and Strategies

The report breaks potential adaptation options into 3
main categories: management, accommodation, and protection. Management includes
zoning policies aimed at discouraging development or rebuilding in high-risk
areas, and the reclamation of flood-prone lands. Accommodation—currently the
most common approach in Virginia—includes raising buildings and roads,
establishing evacuation routes and warning systems, and creating or enhancing storm-water
systems. Protection measures include levees, seawalls, and tidal gates, as well
as “soft-engineering” structures such as living shorelines and created marshes.

The report notes that no single adaptation strategy (other
than abandonment) completely removes the risk of flood damage, and thus urges
the use of “multi-level adaptation strategies,” arguing that this approach
would allow the Commonwealth to “decide on priorities and then ‘buy-down’ the
remaining risk using other options.”

This approach can be visualized as a staircase, says Mitchell,
with each step raising a locality’s resilience to its particular flooding risk.

“In highly developed areas, a storm-surge barrier such as a
levee might be the initial adaptation,” says Mitchell, “with subsequent steps to
elevate structures and invest in emergency management. Each step would reduce
risk to some extent, together resulting in lower risk than any single measure.”

“In more rural areas,”
says Hershner, “the initial step might be to regulate new development to keep
it away from floodplains, with additional steps to develop an early warning
system and a detailed evacuation plan.”

They note that combining “hard” infrastructure, like a
levee, with “soft” infrastructure, like a created marsh, can protect while
adding to the quality of life for local residents. “Created marshes, nourished beaches,
and other open spaces can beautify and contribute recreational and economic value
while still providing flood protection,” says Mitchell.

In sum, the authors note, “Two of the most important lessons
that can be learned from a review of global adaptation strategies are that a
multi-layered approach to flood prevention is most effective and that when
predictions of the future are uncertain, flexible plans for adaptation are
imperative.”

“The challenge in picking the right time horizon,” says
Hershner, “is to be sufficiently long-sighted to prevent future problems, but
still flexible enough to react as knowledge and circumstances change.”

Budgetary, Legal and Technical Issues

In terms of funding the planning and implementation
activities needed to reduce Virginia’s coastal flooding risk, the report
recommends state authorization and support, with cost-benefit studies to help
prioritize projects.

“We encourage local cost-benefit studies followed by state
prioritization of different strategies,” says Hershner. “Questions of state
versus local funding should be included as part of the economic analyses.”

The report also recommends that the Commonwealth should “request
an expert review of local government legal authority to address current and
projected flooding risks and what levels of evidence are likely to be required
to justify locality action.”

Hershner says this recommendation is based on concerns with
Virginia’s Dillon Rule, which holds that localities only have the authorities
specifically given to them by the state.

“The Dillon Rule becomes a significant factor when looking
at how local governments can respond to sea-level rise,” says Hershner. “ As
localities attempt to change development patterns through zoning and building
codes, their actions may be subject to a constitutional challenge under the
Dillon Rule. After expert review, we recommend that the State should enact any
enabling authority needed to allow localities to address current and projected
flooding issues.”

A second concern is that all but one of the agencies
involved in planning for sea-level rise currently use past conditions to
predict the future—and thus cannot incorporate the growing evidence that the
rate of sea-level rise is increasing.

“This is like driving by looking in your rear-view mirror,”
says Hershner. “With the exception of the US Army Corps of Engineers, all of the
statutes and regulations rely on a retrospective analysis of flooding and sea-level
rise. FEMA’s 100-year floodplains, rates of shoreline recession under the
primary dune regulations, and all of the other regulatory analyses don’t
anticipate future conditions. Until these statutes and regulations become
prospective and look to future conditions, they are of little use in adapting
to coastal flooding and sea-level rise.”

The report includes numerous maps showing areas of potential
flooding in light of sea-level rise. The maps assume a 1.5-foot rise in sea
level and a 3-foot storm surge. These represent moderate assumptions, with the
value of sea-level rise well within the range of the best available forecasts
for Virginia over the next 20 to 50 years.

One way to make these maps more accurate, say the report
authors, is to continue to update existing coastal elevation maps using LIDAR,
a high-resolution mapping technique that uses laser light to gauge ground
elevation.

“LIDAR data allow for more precise estimations of elevation,”
says Mitchell, “That helps us better visualize the flooding risk, and improve
the predictive capability of models.”